Question: OK, you’ve mentioned Heller, and I should say it was very kind of you to mention my assistance with your dissent in that case. I was going to ask you to talk a little bit about why, of all of the cases that you participated in during your time on the court, Heller is the one that still keeps you up at night.

Justice Stevens: It’s just a recurring problem that confronts us almost — if not on a daily basis, then at least on a weekly basis. These mass shootings are peculiar to America and are peculiar to a country that has the Second Amendment. So I think that interpreting the Second Amendment to protect the individual right to own firearms is really just absurd, and it’s also terribly important. It happens over and over and over again. I think I should have been more forceful in making that point in my Heller dissent. I don’t blame you any more than I blame myself for failing to place more emphasis on that point.

It’s a characteristic of American society that is not shared by any other civilized country. I find it really mind-boggling that my suggestion that we ought to approach the problem by just getting rid of the Second Amendment really has not captured more popular support, because it’s so obvious that it’s an undesirable part of our government structure.

Question: When Heller was decided, there were people who argued that whether it was correct or incorrect, it was a victory for originalism, because not only Justice Antonin Scalia’s majority opinion, but also your dissent engaged very extensively with founding-era materials. I was going to ask you to explain why you decided to fight so much of the Heller opinion on originalism’s terrain.

Justice Stevens: I didn’t really think at the time or I don’t think now that the question of whether originalism is sound constitutional interpretation had any particular relevance to the outcome of that case. We’re trying to understand what the draftsmen of the provision intended, and a lot of the evidence depends on the fact that New York and Philadelphia and Boston had local laws that would have been unconstitutional under the amendment as construed today. That’s the point that Justice Breyer made so effectively in his dissent. I didn’t think of it in terms of whether we were fighting an originalist battle or just a common-sense battle.

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You don't have to care, but he's one of the few "honest" liberals that is willing to explicitly call for the repeal of the 2nd.

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Why should we care what he says..... he gave up his right to an opinion when he retired...

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The current sitting Justices often times consult with the past sitting Justices, been going on since the beginning lawyers are always consulting with each other and at the root, that is all they are.  Stevens is just trying to assert more information that his current retired status allows him.

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I think occasionally retired SCOTUS justices have also participated in 3-judge panels to hear a case or two in the circuit courts.
O'Connor comes to mind, IIRC.